It is not required by the funeral liturgy, but there shouldn’t be a problem to include it. Make the request to the celebrant of your mother’s funeral liturgy; it should be possible to accommodate your request. After all, at the late John Paul II’s funeral, the litany was chanted and the traditional “Pray for us” was even slightly altered to “Pray for him.”
Our prayers are with you and your family at this difficult time. May your mother rest in peace. God bless.
